Samba Member
Joined: April 11, 2006
Posts: 310
Location: Upland, Ca
 Posted: Fri May 11, 2018 4:12 pm Post subject: Electric fuel pump relay wiring. |  |
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| Hi, I been doing research on wiring an electrical fuel pump including a relay, I remember seeing one diagram that included the oil pressure switch but now I can't find it. Anybody have seen it? Thanks!! 2017 Tiguan 2015 Passat TDI '72 Convertible Under Construction | |
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Samba Member
Joined: April 11, 2006
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Location: Upland, Ca
| Posted: Fri May 11, 2018 7:13 pm Post subject: Re: Electric fuel pump relay wiring. | | ||
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Haven't. Not the diagram that I was looking for but by far the better to read; Thanks!! 2017 Tiguan 2015 Passat TDI '72 Convertible Under Construction | |||
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Joined: January 24, 2006
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Location: Lefty, CA
| Posted: Fri May 11, 2018 9:05 pm Post subject: Re: Electric fuel pump relay wiring. | |
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| There are many different ways to add a safety factor to our electric fuel pumps. I have three different VWs that I cycle through. It is pretty much a given, that when I go to drive the next one, The carburetor bowls (they're all dual carbed) will be empty. What I like about using the rabbit relay, is that I don't have to add any extra switches to fill the carbs. The rabbit relay only sends a signal to the fuel pump when it receives a voltage pulse as the points open and close. So when the engine dies / shutoff, no pulse to the fuel pump. However, with empty carb bowls, as you crank the engine over, it quickly fills the carb bowls. In fact it does it much quicker then a mechanical pump does. I personally like it better then the oil light method. However, probably the safest method would be to use an inertia switch that would kill the pump when an impact / collision is detected. | |
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Joined: April 11, 2006
Posts: 310
Location: Upland, Ca
| Posted: Sat May 12, 2018 4:04 pm Post subject: Re: Electric fuel pump relay wiring. | |
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| I tried this today and it doesn't work, the blue wire from the regulator is negative from the regulator. 2017 Tiguan 2015 Passat TDI '72 Convertible Under Construction | |
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| Posted: Sat May 12, 2018 6:41 pm Post subject: Re: Electric fuel pump relay wiring. | | ||
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His drawing is for the Type IV I believe. May have to adjust to get the same result. This thread is particularly timely as I'm close to finishing my 1835 and I'm using a rotary electric fuel pump and was just starting to think about a safety shutoff. | |||
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Joined: January 24, 2006
Posts: 5071
Location: Lefty, CA
| Posted: Sun May 13, 2018 2:50 am Post subject: Re: Electric fuel pump relay wiring. | |
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| That system will not work for you because a Type 4 alternator works different then your charging system. Here is a pic, and I'll try to explain. On a Type 4, when the key is turned on, the voltage of the battery (12V) is sent through the warning light (T1a - blue wire) to the field of the alternator (C). The light is lit and the alternator is primed to start producing voltage. Then, once the engine is running, the alternator starts to generate its voltage (up to 14.4V). This voltage is sent to the battery (B+), AND back up to the warning light (T1a - blue wire). Since the alternator voltage is higher than the battery voltage, it cancels out the warning light voltage and the warning light goes out. Also, since the (T1a - blue wire) is now carrying a high voltage, it can be used to control a relay. However, your charging system does not work like this, nor does the oil light. This is a rather different system. In fact the warning light BULB is super critical. If it burns out, then the alternator field windings will not be charged, and the alternator will not work at all. Even though I put my fuel pump on a Type 4 engine, I used the Rabbit relay. It is universal, and I don't want to have a burned out light bulb leave me stranded. | |
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Joined: August 17, 2004
Posts: 4103
Location: Oklahoma City, OK
| Posted: Sun May 13, 2018 4:09 am Post subject: Re: Electric fuel pump relay wiring. | |
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| You need to get a VDO 240-850 tee and a oil pressure safety switch it will have three connectors C/NO/NC. The tee screws into the case, your current oil pressure switch screws into the the female 10x1 opening and the safety switch screws into the 1/8-27 female opening on the tee. Wiring is simple, plenty of diagrams online, I would also use a SPST relay. If you do not find a drawing let me know I make one and post it. | |
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| Posted: Sun May 13, 2018 12:31 pm Post subject: Re: Electric fuel pump relay wiring. | |
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| Between the two, I like flat4's option better. It is virtually identical to the Rabbit relay. However, it comes prewired, so nothing else to buy, you'll get instructions, so no guessing. Yes if done correctly, you can use the oil light method. I guess I am just leary from seeing so many PO hacked electrical systems. _________________ 69 road Bug 2110 73 Squareback - 2L, T4, Automatic W/ AC Gone, but many fond memories 69 Baja Bug 2010 - 5 Rib Bus Transaxle Gone but not forgotten 72 Baja Bug 2010 My builds T4 into Squareback http://www.thesamba.com/vw/forum/viewtopic.php?t=458944&highlight= Auto Trans Rebuild http://www.thesamba.com/vw/forum/viewtopic.php?t=516066&highlight= AC in Squareback https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight= | |
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| Posted: Tue May 15, 2018 2:43 pm Post subject: Re: Electric fuel pump relay wiring. | | ||
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It turns positive when the generator is producing electricity. | |||
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Joined: October 13, 2018
Posts: 18
Location: The Ozark Hills area, Missouri
| Posted: Mon Jun 17, 2019 12:40 pm Post subject: Re: Electric fuel pump relay wiring. | |
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| I've been all over trying to understand how to install a relay so that my electric fuel pump will stop when the engine quits turning. I'm a noob with electrical and I'm utterly confused. I have a hard start relay I was told to use for this purpose. It has terminals 30, 85, 86, 87, 87a. My fuel pump is connected to fuse #1 under the dash. Can someone break down this install potato-head style? Everything I've read is going over my head. _________________ 1966 Beetle, daily driver. Former love affairs- '65, '69, '74 Beetle, '74 Thing, '78 Westy. | |
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| Posted: Tue Jun 18, 2019 8:53 am Post subject: Re: Electric fuel pump relay wiring. | | ||
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The Hard Start Relay (which is typically a Bosch-style SPDT relay) is not the best relay for use as a fuel pump relay, but if it is all you have... give this thread a read: https://www.thesamba.com/vw/forum/viewtopic.php?t=712158 The above thread has this diagram: This relay and the way it is wired has a few different states:
2) The ignition is ON + the engine is OFF (alternator lamp is ON) = The relay is powered but current from the ignition switch is being routed to the push button (prime switch) which is OPEN. The fuel pump is OFF because the prime button is preventing current from reaching the pump. 3) The ignition is ON + the engine is OFF (alternator lamp is ON) + prime button is pressed = This passes 12v to the fuel pump while the prime button is pressed. This allows you to pre-fill the carb fuel bowl before you try to crank the engine. This may not always be needed (there is usually some fuel in the carb), but is a nice option to have when you believe the fuel bowl is completely/mostly empty. As long as the carb inlet valve is working and the fuel pump pressure is not too high, there is no harm pressing the button. If you wanted to get creative you could replace the prime button w/ a circuit that closes the circuit for a few seconds each time it is powered to automatically prime the carb. 4) The ignition is ON + the engine is ON (alternator lamp is OFF) = The relay is OFF, but current from the ignition is now being routed to the fuel pump over the 87a wire. This can happen WHILE cranking the engine if the GEN lamp were to go OUT before the engine started running on its own. But not all engines will generate enough voltage while cranking to turn off the GEN lamp. If this is your case, the fuel pump will not turn ON until the engine is running and the GEN lamp has turned OFF. This is the reason for the prime button. It allows you to run the pump before the engine is running. The beauty of this circuit is it does not drain power while the engine is running but also does not drain power when the ignition is OFF. The only time is draws power (and very little) is in that short period when the ignition is ON and the engine is NOT running. Any time the GEN lamp turns ON the power to the fuel pump is cut to prevent a fire hazard. As an alternate way to wire this, you could connect the #86 terminal to the Oil Pressure switch wire. This is also grounded when the engine is not running so would function the same. If you read the above thread, there is a specialized relay just for fuel pumps (Amazon.com link in the thread). This relay pre-primes the pump automatically when the ignition is turned on and provides a similar level of protection when the engine turns OFF. If you don't already have a relay, this is probably the ideal option. | |||
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} Sofa King
Joined: May 18, 2007
Posts: 375
Location: Auburn, WA
| Posted: Tue Jun 18, 2019 1:43 pm Post subject: Re: Electric fuel pump relay wiring. | | ||
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Do this. This is a great resource for electrical stuff. The old Speedy Jim Page. http://www.nls.net/mp/volks/htm/elec.htm http://www.nls.net/mp/volks/htm/elec.htm | |||
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Joined: October 13, 2018
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Location: The Ozark Hills area, Missouri
| Posted: Tue Jun 18, 2019 4:13 pm Post subject: Re: Electric fuel pump relay wiring. | |
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| You guys are great! I'd love to do anything like those diagrams but it might as well be Greek. I have zero electrical experience other than what I've read... which seems to have made things more confusing. Please tell me, am I reading this thing correctly? I'm not using a push button to bypass- so leave 87a empty? Former love affairs- '65, '69, '74 Beetle, '74 Thing, '78 Westy. | |
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Joined: February 16, 2007
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Location: North Florida, USA
| Posted: Wed Jun 19, 2019 7:06 am Post subject: Re: Electric fuel pump relay wiring. | | ||||
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Diagrams are the BEST way to communicate how to wire things. There is no ambiguity in a pic with a wire running from a numbered terminal to ground or power. But words can be confusing when it comes to wiring. Example, �Place the relay between a 12v ignition switch source and ground using terminals #85 & #86.�
These two descriptions come from BOTH of the above diagrams. Which of the two diagrams are you planning to use? You need to pick one. If you leave the prime button out... you run the risk of getting stranded when your carb fuel bowl runs dry and you have no way to fill it with fuel before starting the engine. If your GEN lamp goes out WHILE cranking the engine then maybe you don�t need the prime button. When the GEN light goes out with the ignition ON (engine running) both systems above will drive the fuel pump. But if your GEN lamp remains ON until AFTER the engine is running then your carb will never prime and you will get stuck. Take time to look over the diagram you choose to use. If you really want to delete the prime button just remove the prime button and the wires running to it. No offense, but if you cannot read the above two diagrams you probably shouldn�t be trying to do your fuel pump wiring yourself. Leave it for a skilled friend of mechanic to do. The above diagrams are not super simple and require a moderate understanding of wiring. Wire the relay wrong and it will remain ON all the time and creates a risk that the pump will overflow the carb and flood the engine. Or best case, it kills your battery. | |||||
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